1. Field of the Invention
The present invention relates to resin ceramic compositions. More particularly, the resin ceramic compositions of the invention include a ceramic that provides the composition with magnetic properties.
2. Description of the Prior Art
A variety of resins are used in connection with devices having magnetic or electronic uses. Often the resin serves as a package or as a support structure onto which other devices are attached. Hence, the resin must be further processed to provide a finished product.
Semiconductor devices are packaged and encapsulated in a variety of resinous materials, including epoxy. Epoxy resins have excellent heat resistance, moisture resistance, electrical characteristics and adhesion properties, and they can acquire various characteristics with the addition of modifying agents. Accordingly, epoxy resins are used for packaging microelectronic components, such as integrated circuits.
The epoxy compositions used in electronic applications may include a hardener and fillers. The fillers are utilized to provide the epoxy resin with desirable characteristics such as a low coefficient of thermal expansion and high thermal conductivity. Commonly used fillers include inorganic fillers used in combination with epoxy include silica, quartz, alumina, fiber glass, calcium silicate, a variety of earths and clays, and combination thereof. Examples of epoxy compositions which include various types of fillers which are used in electronic applications are described in U.S. Pat. No. 4,042,550.
One type of semiconductor device which utilizes epoxy compositions, are proximity sensing devices, such as a Hall effect sensor. A Hall effect sensor relies on a change of magnetic flux density applied to a sensing plane of a Hall effect element. A detailed description of Hall effect sensors is set forth in U.S. Pat. Nos. 5,729,130, 5,694,038, 5,650,719, 5,389,889 and 4,970,463, and the operation of a number of different Hall effect type sensors is described in Allegro (formerly Sprague) Data Book SN-500.
In a representative Hall effect sensor as shown in U.S. Pat. No. 4,970,463, a magnet is mounted a fixed distance from a sensing plane of a Hall effect sensor element, defining an air gap and forming an assembly. The manufacture of such assemblies requires that the magnet be mounted in a particular orientation relative to the sensing plane. Various techniques are known for fixing the position of the Hall effect sensor, such as potting or overmolding. In one known overmolding technique, the magnet is overmolded onto an existing semiconductor which is already encapsulated in a package. The addition step of adding or overmolding a magnet to the semiconductor increases the complexity and cost of manufacture of such devices.
In addition to the increased manufacturing cost, a common shortcoming of such sensing devices is the dependence of the output of the device on the airgap between the device and the magnet which may vary on a part to part basis. More specifically, as the air gap between the magnet and the semiconductor increases, the maximum output range of the device decreases, decreasing the sensitivity of the sensor. Thus, there is a need to provide a reduced cost Hall effect sensor with relatively consistent repeatable output characteristics.